U.S. patent application number 11/470747 was filed with the patent office on 2008-04-03 for apparatus, system and method for identification with temperature dependent resistive device.
Invention is credited to John Philip TAYLOR.
Application Number | 20080079446 11/470747 |
Document ID | / |
Family ID | 39157828 |
Filed Date | 2008-04-03 |
United States Patent
Application |
20080079446 |
Kind Code |
A1 |
TAYLOR; John Philip |
April 3, 2008 |
APPARATUS, SYSTEM AND METHOD FOR IDENTIFICATION WITH TEMPERATURE
DEPENDENT RESISTIVE DEVICE
Abstract
An apparatus, system, and method provide device identification
and temperature sensing of a device with a temperature sensing
circuit (TSC) within the device. The TSC includes a temperature
sensing element (TSE) connected in parallel with a voltage clamping
network (VCN) that limits the voltage across the TSE to an
identification voltage within an identification voltage range when
the voltage is greater than or equal to a lower voltage of the
identification voltage range. When a voltage below the lower range
is applied to the TSC, the VCN appears as an open circuit and the
resistance of the TSC corresponds to temperature. For cost or other
concerns, a first TSC may omit the VCN to provide a maximum
identification voltage and other TSCs may include VCNs with lower
identification voltage ranges.
Inventors: |
TAYLOR; John Philip; (San
Diego, CA) |
Correspondence
Address: |
KYOCERA WIRELESS CORP.
P.O. BOX 928289
SAN DIEGO
CA
92192-8289
US
|
Family ID: |
39157828 |
Appl. No.: |
11/470747 |
Filed: |
September 7, 2006 |
Current U.S.
Class: |
324/721 ;
374/E1.005; 374/E7.018 |
Current CPC
Class: |
G01K 7/16 20130101; G01K
1/026 20130101 |
Class at
Publication: |
324/721 |
International
Class: |
G01R 27/08 20060101
G01R027/08 |
Claims
1. A temperature sensing circuit comprising: a temperature sensing
element; and a voltage clamping network connected in parallel to
the temperature sensing element, the voltage clamping network
configured to limit a voltage across the voltage clamping network
to an identification voltage range when the voltage is greater than
or equal to a lower voltage of the identification voltage
range.
2. The temperature sensing circuit of claim 1, wherein the voltage
clamping network comprises a diode arrangement.
3. The temperature sensing circuit of claim 2, wherein the diode
arrangement comprises a Zener diode.
4. The temperature sensing circuit of claim 2, wherein the diode
arrangement comprises a plurality of diodes connected in
series.
5. The temperature sensing circuit of claim 2, wherein the diode
arrangement comprises an active Zener diode.
6. The temperature sensing circuit of claim 5, wherein the active
Zener diode is one of a plurality of active zener devices
configured to provide one of a plurality of clamping voltages.
7. The temperature sensing circuit of claim 2, wherein the voltage
clamping network comprises an identification resistor connected in
series with the diode arrangement.
8. The temperature sensing circuit of claim 7, wherein the
identification resistor is one of a set of identification
resistors, each identification resistor corresponding to one of a
plurality of identification voltage ranges.
9. A temperature measuring and identification (TMID) device
comprising: a voltage source connected to a detection port through
a limiting resistor; a current source connected to the detection
port; and a controller configured to identify a temperature
measuring circuit connected to the detection port from a plurality
of temperature measuring circuits based on a first measured voltage
at the detection port when the voltage source provides an output
voltage resulting in a first measured voltage above an upper
voltage of a temperature measuring voltage range and configured to
determine a temperature of the temperature sensing circuit based on
a second measured voltage at the detection port when the voltage
source is off.
10. The TMID device of claim 9, wherein the current source
comprises a bias resistor connected to a supply voltage, the bias
resistor connected in series with the temperature sensing element
when the identification device is connected to the detection
port.
11. The TMID device of claim 9, the voltage source comprising a
general purpose input/output (GPIO) port of a processor, the GPIO
port providing the output voltage in an output state and providing
an open circuit when the GPIO is an off state.
12. The TMID device of claim 11, further comprising: an analog to
digital converter (ADC) connected to the detection port and
configured to provide a first digital value corresponding to the
first measured voltage and a second digital value corresponding to
the second measured voltage.
13. The TMID device of claim 12, the controller configured to
determine that the temperature measuring circuit has a first
identification value when the first measured voltage is within a
first identification voltage range and to determine that the
temperature circuit has a second identification value when the
first measured temperature is within a second identification
voltage range.
14. The TMID device of claim 12, wherein the first measured voltage
is equal to a voltage clamp voltage within a clamp voltage range of
a voltage clamp circuit connected in parallel to a temperature
sensing element within the temperature measuring circuit.
15. A device identification system comprising: a plurality of
temperature sensing circuits, at least some of the temperature
sensing circuits comprising a temperature sensing element and a
voltage clamping network connected in parallel to the temperature
sensing element, the voltage clamping network configured to limit a
voltage at a connector to an identification voltage range when the
voltage is greater than or equal to a lower voltage of the
identification voltage range; and a temperature measuring and
identification (TMID) device having a detection port configured to
connect the connector of each of the plurality of temperature
sensing circuits, the TMID device comprising: a voltage source
connected to a detection port through a limiting resistor; a
current source connected to the detection port; and a controller
configured to identify a connected temperature measuring circuit
connected to the detection port from the plurality of temperature
measuring circuits based on a first measured voltage at the
detection port when the voltage source provides an output voltage
resulting in a first measured voltage above an upper voltage of a
temperature measuring voltage range and configured to determine a
temperature of the connected temperature sensing circuit based on a
second measured voltage at the detection port when the voltage
source is off.
16. The identification system of claim 15, wherein the plurality of
temperature sensing circuits comprises a first set of temperature
sensing circuits corresponding to a first identification value and
a second set of temperature sensing circuits corresponding to a
second identification value.
17. The identification system of claim 16, wherein each of the
temperature sensing circuits of the first set comprises the
temperature sensing element and wherein each of the temperature
sensing circuits of the second set comprises the temperature
sensing element and a second set voltage clamping network connected
in parallel to the temperature sensing element, the second set
voltage clamping network configured to limit the voltage at the
connector to a second set identification voltage range when the
voltage is greater than or equal to a lower voltage of the second
set identification voltage range.
18. The identification system of claim 17, wherein the plurality of
temperature sensing circuits further comprises a third set of
temperature sensing circuits corresponding to a third
identification value.
19. The identification system of claim 18, wherein each of the
temperature sensing circuits of the third set comprises the
temperature sensing element and a third set voltage clamping
network connected in parallel to the temperature sensing element,
the third set voltage clamping network configured to limit the
voltage at the connector to a third set identification voltage
range when the voltage is greater than or equal to a lower voltage
of the third identification voltage range, the third set voltage
clamping network comprising a voltage clamping device connected in
series with an identification resistor.
20. The identification system of claim 19, wherein the plurality of
temperature sensing circuits further comprises a fourth set of
temperature sensing circuits corresponding to a fourth
identification value, each of the temperature sensing circuits of
the fourth set comprising the temperature sensing element and a
fourth set voltage clamping network connected in parallel to the
temperature sensing element, the fourth set voltage clamping
network configured to limit the voltage at the connector to a third
set identification voltage range when the voltage is greater than
or equal to a lower voltage of the third identification voltage
range, the fourth set voltage clamping network comprising the
voltage clamping device connected in series with another
identification resistor.
Description
TECHNICAL FIELD
[0001] The invention relates in general to temperature dependent
resistive devices and more specifically to an apparatus, system,
and method for identification with temperature dependent resistive
devices.
BACKGROUND
[0002] Many systems and circuits utilize temperature sensing
elements (TSEs) to determine a temperature of a device. For
example, typical temperature dependent resistive devices (TDRD)
such as thermistors may have resistances that are inversely
proportional to temperature. By measuring the resistance of the
thermistor, the temperature of the thermistor can be determined. As
a result, temperatures of components and devices near the
thermistor can also be determined or estimated. Resistance sensing
techniques are sometimes used as identification techniques to
determine the identity of a device, module, or other peripheral
unit that is connected to a main device or main assembly. For
example, portable communication devices that accept more than one
type of modular battery include a battery identification technique
to determine the type of battery that is connected to the portable
communication device. In order to minimize components and contacts,
conventional designs often combine temperature sensing techniques
and identification techniques. For example, some conventional
portable communication devices that accept more than one type of
modular battery include a temperature sensing mechanism that
connects to circuits within the battery packs to determine
temperature and to identify the battery module. Each type of
battery module includes thermistor circuits having different
characteristics allowing the portable communication device to
identify the particular battery module that is connected.
Typically, each thermistor circuit has a resistance to temperature
relationship that is offset from relationships of other thermistor
circuits within other types of battery modules. Conventional
systems are limited, however, in that the resistance-to-temperature
relationships of different circuits typically overlap. FIG. 1, for
example, is a graphical illustration showing two curves 102, 104
representing the resistance vs. temperature relationship for two
conventional battery modules where the curves overlap. The overlap
region 106 results in ambiguous data since a measurement of a
resistance within the overlap region is associated with both of the
curves 102, 104. The measurement may correspond to one type of
battery module at a low temperature or another type of battery
module at a higher temperature. For example, resistance R may
correspond to a temperature of T1 if one battery module is used and
a temperature of T2 if another battery is connected. This error
could lead to catastrophic results. A battery could explode where a
battery module is inaccurately identified and an incorrect charging
scheme is applied. Further, the dynamic range and accuracy of the
temperature measuring circuit is reduced as the number of
identification devices is increased as well as requiring a unique
voltage to temperature transfer function for each of the possible
curves. In addition, these problems are exacerbated as the number
of IDs is increased.
[0003] Accordingly, there is a need for an apparatus, system and
method for identification with temperature dependent resistive
devices.
SUMMARY
[0004] An apparatus, system, and method provide device
identification and temperature sensing of a device with a
temperature sensing circuit (TSC) within the device. The TSC
includes a temperature sensing element (TSE) connected in parallel
with a voltage clamping network (VCN) that limits the voltage
across the TSE to an identification voltage within an
identification voltage range when the voltage is greater than or
equal to a lower voltage of the identification voltage range. When
a voltage below the lower range is applied to the TSC, the VCN
appears as an open circuit and the resistance of the TSC
corresponds to temperature. For cost or other concerns, a first TSC
may omit the VCN to provide a maximum identification voltage and
other TSCs may include VCNs with lower identification voltage
ranges.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a graphical illustration of a resistance to
temperature relationship of two conventional identification and
temperature sensing circuits.
[0006] FIG. 2 is a block diagram of a temperature sensing circuit
(TSC) connected to a measuring temperature measuring and
identification device (TMID device) in accordance with the
exemplary embodiment.
[0007] FIG. 3 is a graphical illustration of the voltage (V.sub.DP)
at the detection port during measuring, diagnostic, and
identification procedures.
[0008] FIG. 4 is a schematic representation of an exemplary
implementation of the temperature measuring and identification
device (TMID device) where the voltage source, the voltage sensor,
and the controller are implemented within a processor.
[0009] FIG. 5 is a schematic representation of an equivalent
circuit of a TMID device connected to a TSC that does not include a
VCN.
[0010] FIG. 6 is a schematic representation of an equivalent
circuit of a TMID device connected to a TSC having a VCN that
includes only a voltage clamping device.
[0011] FIG. 7 is a schematic representation of an equivalent
circuit of a TMID device connected to a TSC having a VCN that
includes a voltage clamping device in series with an identification
resistor (R.sub.ID).
[0012] FIG. 8 is a block diagram of a plurality of temperature
sensing circuits (TSCs) of an identification system including four
identification values (IDs).
DETAILED DESCRIPTION
[0013] FIG. 2 is a block diagram of a temperature sensing circuit
(TSC) 202 connected to a temperature measuring and identification
(TMID) device 204 to form a temperature measuring and
identification circuit 200. As discussed in further detail below,
the TSC 202 is one TSC of a set of TSCs where the characteristics
of the TSCs allow the TMID device 204 to distinguish between the
different sets of TSCs. The TSCs can be installed within different
devices providing a mechanism for monitoring the temperature of a
device and for identifying the device. An example of suitable
application of the temperature measuring and identification circuit
200 includes installing a different TSC within each type of battery
module accepted by a portable device. The TMID device 204 can be
implemented as part of portable device to identify different types
of battery modules and to determine the temperature of the battery
module.
[0014] Each TSC 202 includes at least a temperature sensing element
(TSE) 208. At least one TSCs of a TSC set includes a voltage
clamping network (VCN) 206 connected in parallel to the TSE 208. In
the exemplary embodiment, a linearization resistor (not shown in
FIG. 2) is also connected in parallel to the TSE 208 in all of the
TSCs in order linearize the temperature to resistance curves of the
TSC 202.
[0015] The TMID device 204 connects to the TSC 202 through a
connection interface 210 that includes at least a detector port
212. The connection interface 210 may include any of numerous types
of connectors, contacts, or electrical connection mechanisms to
provide an electrical connection between the TMID device 204 and
the TSC 202. The exemplary connection interface 210 also includes a
ground connector. Additional contacts may be used for other signals
in some circumstances.
[0016] As described below, each set of TSCs of the plurality of
TSCs includes a different VCN where the VCN may include any
combination of resistors and/or voltage clamping devices, such as
diodes. The VCN may be omitted from a TSC to create an
identification value (ID) that is not voltage clamped. When the TSC
is connected to the TMID device 204, the voltage at the detection
port 212 depends on the particular VCN 206, the temperature, and
the status of voltage source 214 in the TMID device 204. The VCN
limits the detector port voltage to a voltage within an ID voltage
range. The number of ID voltage ranges depends on the number of TSC
sets that can be connected to the TMID device 204.
[0017] The TMID device 204 includes a voltage source 214 connected
to the detection port 212 through a limit resistor 216, a current
source 218 connected to the detection port 212, and voltage sensor
220 connected to the detection port 212. A controller 222 is
configured to control the voltage source 214 and to receive a
voltage measurement from the voltage sensor 220. Based on the
voltage measurement and the status of the voltage source 214, the
controller 222 determines the temperature of the TSE 208 and an ID
of the TSC 200 from a plurality of IDs. As discussed below, the
voltage source 214, voltage sensor 220, and the controller 222 are
implemented within a processor in the exemplary embodiment. The
current source 218 is any arrangement of components or devices that
provide a known current to the detection port 212. In the exemplary
embodiment, a bias resistor (not shown in FIG. 2) is connected to
the voltage supply (Vdd) of the TMID device 204 to form the current
source 218.
[0018] The TMID device 204 controls the voltage source 214 to
switch the voltage source 214 on and off. The voltage source 214
provides an output voltage in the "on" state and appears as a high
impedance (open circuit) in the "off" state. When the voltage
source 214 is off, the current source 218 provides the only current
to the detection port 212. In this state, the voltage (V.sub.DP)
measured by the voltage sensor 220 at the detection port 212 is
processed by the controller 222 to determine the temperature of the
TSE 208 or to determine that an error condition exists. Where the
detected voltage is within a temperature measuring voltage range,
the voltage (V.sub.DP) at the detection port corresponds to the
resistance of the TSE 208 and the controller 222 calculates the
temperature based on the detected voltage. If the voltage is
outside the range, the controller 222 determines that an error
condition exists. When the voltage source 214 is turned on, the
voltage at the detection port (V.sub.DP) is established by the
current from the current source 218 and the current from the
voltage source 214. If the voltage is above the temperature
measuring voltage range, the controller 222 determines the
identification value (ID) of the TSC based on the voltage
(V.sub.DP). If the voltage is below the temperature measuring
range, the controller 222 determines that an error condition
exists.
[0019] FIG. 3 is a graphical illustration of the voltage (V.sub.DP)
at the detection port 212 during measuring, diagnostic, and
identification procedures. The various values and ranges depicted
in FIG. 3 are not necessarily to scale and are provided to
generally illustrate relationships between different voltages and
temperatures during different conditions.
[0020] During the temperature measuring procedure, the voltage
source 214 is turned off and the voltage (V.sub.DP) indicates a
temperature or an error condition. If the voltage (V.sub.DP) is
above an upper temperature measuring voltage (V.sub.UTM) 302 of the
temperature measuring voltage range (V.sub.MR) 304, the controller
222 determines that no TSC 202 is connected to the TMID device 204.
If the voltage (V.sub.DP) is at or near the supply voltage (Vdd) of
the TMID device 204, for example, the voltage indicates that no
current is flowing through the detection port 212 and that no
circuit is connected to TMID device 204. If the voltage is below a
lower temperature measuring voltage (V.sub.TLM) 308 of the
temperature measuring voltage range (V.sub.MR) 304, the controller
222 determines that something other than a valid and properly
operating TSC is connected to the TMID device 204. For example, a
voltage near zero can indicate a short circuited detection port 212
that may be due to a failed TSC or an invalid TSC device that is
not intended to be connected to the TMID device 204. If the voltage
is within the temperature measuring voltage range (V.sub.MR) 304,
the voltage (V.sub.DP) corresponds to a temperature of the TSE 202
where the temperature may be measured between a minimum temperature
(T.sub.MIN) 310 and a maximum temperature (T.sub.MAX) 312. In the
exemplary embodiment, where the TSE is an NTC thermistor, a maximum
voltage (VID1) corresponds to the minimum temperature (T.sub.MIN).
The relationship between detector port voltage (V.sub.DP) and
temperature follows a temperature curve 301. The shape of the curve
301 depends on the temperature sensing element (TSE) 208
characteristics as well as other components in the circuit. In the
exemplary embodiment, a linearization resistor is connected in
parallel with the TSE 208 in order to make the curve 301 more
linear as compared to a TSC that includes a TSE without a
linearization resistor.
[0021] When the voltage source 214 is turned on, the voltage
(V.sub.DP) corresponds to an identification value (ID) of the TSC
202 or indicates an error condition. If the voltage is above the
upper temperature measuring voltage (V.sub.UTM) 302, the voltage
indicates the ID of the TSC 202. Otherwise, the voltage indicates
an error condition. For example, a voltage near zero can indicate a
short circuited detection port 212 that may be due to a failed TSC
or an invalid TSC device that is not intended to be connected to
the TMID device 204.
[0022] A measured voltage above the upper temperature measuring
voltage (V.sub.UTM) 302 is associated with one of at least two ID
voltages or ID voltage ranges. The number of voltage IDs depends on
the number of TSCs in the set of TSCs that may be connected to the
TMID device 204. When the voltage source 214 is turned on, the
controller 222 determines the ID of the TSC 202 based on the
voltage (V.sub.DP) at the detection port 212. The voltage source
214, current source 218, and limit resistor 216 are configured to
provide a voltage above the upper temperature measuring voltage
temperature (V.sub.UTM) 302 when the voltage source 214 is on. An
example of a suitable scheme includes having one TSC that does not
include a VCN and that results in a first ID voltage (VID1) that is
near the maximum voltage 306 and that corresponds to a first (ID1),
a second TSC that includes a VCN that limits the voltage near
V.sub.UTM 302 to define a second ID (ID2), and additional TCSs that
include VCNs that result in ID voltage ranges that are between the
ID voltage (VID1) and the second ID voltage (VID2). The maximum
number of ID voltage ranges depends on the available voltage range
between the V.sub.UTM and the maximum voltage 306 as well as the
size of the ID voltage ranges. The maximum voltage 306 is the
voltage corresponding to the minimum temperature since the
thermistor has a maximum resistance at the minimum temperature. As
explained below, the various components are selected such that the
worst case maximum voltage of the thermistor is less than a forward
voltage of the TSE that occurs at the highest operating
temperature.
[0023] FIG. 3 illustrates an exemplary system that supports four
IDs although any combination and number of ID voltages may be used
to group TSCs into ID categories. A first ID voltage 306 results
when a first type TSC that does not include a VCN is connected to
the TMID device 204 and the voltage source 214 is on. A second ID
voltage results within a voltage range 314 when a second type TSC
that includes a VCN is connected to the TMID device 204 and the
voltage source 214 is on. ID voltages result within a third voltage
range 316 and a fourth voltage range 318 when a third type TSC and
a fourth type TSC are connected to the TMID device 204,
respectively. When the voltage sensor 220 indicates a voltage at
the detection port 212 that is within an ID voltage range, the
controller 222 determines that the TSC connected to the TMID device
has an ID corresponding to the ID voltage range. Therefore, the
controller 222 determines that the TSC has one of four IDs for the
scheme illustrated in FIG. 3. As discussed below, the IDs
associated with an ID voltage range correspond to the TSCs that
include VCNs. Since the voltage clamping devices within the VCN,
such as diodes, have a forward voltage threshold that varies
between devices and over temperature, the ID voltage resulting from
a particular TSC may vary from a lower voltage to an upper voltage
of the corresponding ID voltage range. Accordingly, the second ID
voltage range 314 includes a lower voltage (VID.sub.L2) 320 and an
upper voltage (VID.sub.U2) 322, the third ID voltage range 316
includes a lower voltage (VID.sub.L3) 324 and an upper voltage
(VID.sub.U3) 326, and the fourth ID voltage range 318 includes a
lower voltage (VID.sub.L4) 328 and an upper voltage (VID.sub.U4)
330.
[0024] FIG. 4 is a schematic representation of an exemplary
implementation 400 of the temperature measuring and identification
circuit 100 where the voltage source 214, the voltage sensor 220,
and the controller 222 are implemented within a processor 402. The
various components and functions described above with reference to
FIG. 1 can be implemented using other combinations of hardware,
software, and/or firmware. In the exemplary implementation, the
voltage source 214 is a general purpose input/output (GPIO) port
404 of a processor 402. The processor may be any type of general
purpose processor, application specific integrated circuit (ASIC),
or other microprocessor or processor arrangement, that can perform
the function described herein. Code running on the processor 402
facilitates the functions of the controller 222 as well as other
functions of the TMID device 204. The controller 222 controls the
GPIO port 404 to place the GPIO port in an output state and an
input state. In the output state, the GPIO port 404 provides a
voltage at or near the Vdd. In the input state, the GPIO port
presents an open circuit to the detection port 212 through the
limiting resistor (R.sub.LIM) 216. An analog-to-digital converter
(ADC) 406 measures the voltage (V.sub.DP) by providing the
controller 222 a digital representation of the voltage (V.sub.DP)
at the detection port 212. A bias resistor (R.sub.BIAS) 407
connected to the voltage supply (Vdd) provides the current source
218 for temperature measurement.
[0025] Any one of at least two TSCs can be connected to the TMID
device 204. FIG. 4 illustrates a TSC that includes a linearization
resistor (R.sub.LIN) 408, a TSE 208 and a VCN 206, where the TSE
208 is a thermistor 208 and the VCN 206 includes an identification
resistor (R.sub.ID) 410 in series with a voltage clamping device
412. In the exemplary implementation, the voltage clamping device
412 is a diode arrangement 412 that includes one or more diodes
that have a forward voltage within a forward voltage range. The
voltage range depends on the number and type of diodes. For
example, a typical PN junction, silicon diode has a forward voltage
of approximately 0.7 volts. Two silicon diodes in series will have
a collective forward voltage of about 1.4 volts. Due to
manufacturing variations and other factors, the forward voltage of
a particular diode may be greater than or less than the expected
drop. Further, the forward voltage varies over temperature.
Accordingly, a voltage range is defined for the diode arrangement
412 where any particular diode arrangement will have a forward
voltage within the range. Examples of other suitable diode
arrangements include arrangements using single Zener diodes and
active Zener diodes. Zener diodes can be used with reverse bias to
maintain a fixed voltage across their terminals. In addition, the
voltage clamping variations of Zener diodes are typically less than
the forward voltage variations of PN junction silicon diodes over
temperature, bias current and manufacturing variations. Active
Zener diodes may be preferred in some circumstances since active
Zener diodes, also known as "shunt regulators" have variations in
clamping voltages lower than normal Zener diodes.
[0026] For the purpose of temperature measurement, the GPIO port
404 is set to the "Off" state such that current may not flow into
or out of R.sub.LIM 216. In this case, current may only be supplied
by R.sub.BIAS 407 into the TSC 202. The values of R.sub.BIAS 407,
R.sub.LIN 408 and R.sub.THERM 208 are selected such that at the
minimum temperature where R.sub.THERM will exhibit its maximum
resistance, the voltage sensed by the ADC 220 and due to the
resulting voltage divider formed between Vdd 405 and ground 403 is
less than the forward voltage of the diode arrangement 412. The
resulting voltage will only be a factor of the temperature
measurement components R.sub.BIAS 407, R.sub.LIN 408 and
R.sub.THERM 208 which is sensed by ADC 406. The ADC 406 converts
the analog voltage measurement to a digital value that is processed
by the controller 222 as a temperature measurement.
[0027] For the purpose of identification, when the TSC 202 is
connected to the TMID device 204, the processor 402 sets the GPIO
port 404 to an output state that, in the exemplary embodiment, is
powered from the same supply voltage Vdd 405 as the R.sub.BIAS
resistor 406. Accordingly, the limit resistor 216 and the
R.sub.BIAS resistor 407 form an equivalent parallel combination
resistance that is in series with the resistance of TSC 202. The
voltage (V.sub.DP) at the detection port 212 is the output of the
resulting voltage dividing network between the supply Vdd 405 and
ground 403 and is sensed by ADC 406. The ADC 406 that converts the
analog voltage to a digital value that is processed by the
controller 222 as an ID value.
[0028] FIG. 5 is a schematic representation of an equivalent
circuit 500 of a TMID device 204 connected to a TSC 202 that does
not include a VCN. As described above, when the GPIO port 404 is
set to the output state, the limit resistor, R.sub.LIM 216 and the
bias resistor, R.sub.BIAS 407 form an equivalent parallel
combination resistance (R.sub.SEQ) connected to the supply, Vdd
405. The limit resistor, R.sub.LIN 408 and thermistor, R.sub.THERM
208 form an equivalent parallel combination resistance R.sub.TEQ.
The values of the resistors R.sub.LIM 216, R.sub.BIAS 407,
R.sub.LIN 408 and R.sub.THERM 208 are selected such that the value
of R.sub.SEQ 502 is much, much lower than R.sub.TEQ 504 so that a
majority of Vdd 405 is dropped across R.sub.TEQ 504. The ADC 406
will subsequently sense an ID voltage 306 that is the maximum ID
voltage of the set of ID voltages.
[0029] FIG. 6 is a schematic representation of an equivalent
circuit 600 of TMID device 204 connected to a TSC 202 having a VCN
that includes only a clamping arrangement 412. As described above,
when the GPIO port 404 is set to the output state, the limit
resistor, R.sub.LIM 216 and the bias resistor, R.sub.BIAS 407 form
an equivalent parallel combination resistance R.sub.SEQ connected
to Vdd 405. Because of the claming arrangement 412, the voltage
into the ADC 406 does not rise to Vdd 405 as in the previous
example but instead is clamped to the forward voltage of clamping
arrangement 412 resulting in the lowest ID voltage range 314 of the
ID voltage set. The resulting voltage is converted by ADC 406 as
detailed above.
[0030] FIG. 7 is a schematic representation of an equivalent
circuit of a TMID device 204 connected to TSC 202 having a VCN that
includes a clamping arrangement 412 in series with an
identification resistor (Rid) 410. As described above, when GPIO
port 404 is set to the output state, R.sub.LIM 216 and R.sub.BIAS
407 form an equivalent parallel combination resistance, R.sub.SEQ
connected to Vdd 405. Because of the clamping arrangement 412, the
voltage at the ADC 406 does not rise to Vdd 405 and because of the
identification resistor, R.sub.ID 410, the voltage at the ADC 406
is greater than the forward voltage of the diode arrangement 412.
The identification resistor, R.sub.ID 410, is selected such that it
forms a voltage divider between Vdd 405 and the forward voltage of
the diode arrangement 412 when in series with R.sub.SEQ 502. The
resulting voltage is converted by ADC 406 as detailed above.
Accordingly, the ID of the TSC may be changed by adjusting the
value of R.sub.ID 410 such that a third ID voltage range 316
corresponds to a TSC 202 that has an R.sub.ID 410 of one value and
a fourth ID voltage range 318 that has an R.sub.ID 410 with another
value.
[0031] FIG. 8 is a block diagram of a plurality of temperature
sensing circuits (TSCs) 800 of an identification system including
four identification values (IDs) 802, 804, 806, 808. The TSCs of a
first set of TSCs 810 have a first identification value (ID1) 802,
the TSCs of a second set of TSCs 812 have a second identification
value (ID2) 804, TSCs of a third set of TSCs 814 have a third
identification value (ID3) 806, and the TSCs of a fourth set of
TSCs 816 have a fourth identification value (ID4) 808. In the
exemplary system, the TSCs of the first set 810 include only a
temperature sensing element 208 and a linearization resistor 408
and do not include a VCN. Accordingly, ID1 corresponds to the first
voltage ID 306 shown in FIG. 3.
[0032] The TSCs of the second set 812 include a temperature sensing
element 208, a linearization resistor 408, and a VCN 818 that
includes a voltage clamping device 412. The VCN 818 does not
include an identification resistor 410. Accordingly, the second ID
corresponds to the second ID voltage range 314.
[0033] The TSCs of the third set 814 include a temperature sensing
element 208, a linearization resistor 408, and a VCN 818 that
includes a voltage clamping device 412 and an identification
resistor 410 having a first ID resistance 822. The third ID
corresponds to the third ID voltage range 316.
[0034] The TSCs of the fourth set 816 include a temperature sensing
element 208, a linearization resistor 408, and a VCN 824 that
includes a voltage clamping device 412 and an identification
resistor 410 having a second ID resistance 826. The fourth ID
corresponds to the fourth ID voltage range 318.
[0035] The values of the components of the TSC 202 and the TMID
device 204 are selected based on the number of IDs, the desired
temperature measuring range, the supply voltage and other factors.
Typically, the worst case upper voltage limit corresponds to the
minimum temperature of a negative temperature coefficient (NTC)
thermistor. Accordingly, the values of the components are selected
such that the worst case upper voltage limit is less than the
lowest forward voltage limit of the voltage clamping device 412
(diode arrangement) which typically occurs at the highest
temperature due to the negative temperature coefficient of the
diode. The maximum dynamic range for a temperature measurement can
be achieved by using an appropriately low reference during the
temperature conversion.
[0036] Clearly, other embodiments and modifications of this
invention will occur readily to those of ordinary skill in the art
in view of these teachings. The above description is illustrative
and not restrictive. This invention is to be limited only by the
following claims, which include all such embodiments and
modifications when viewed in conjunction with the above
specification and accompanying drawings. The scope of the invention
should, therefore, be determined not with reference to the above
description, but instead should be determined with reference to the
appended claims along with their full scope of equivalents.
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